Process for stabilizing red phosphorus



Patented Apr. 28, 1953 OFFICE,

PROCESS FOR STABILIZING RED PHOSPHORUS George F. Nordblom, Philadelphia, Pa.

No Drawing. Application March 13, 1945, Serial No. 582,479

10 Claims. (01. 2s---22s) (Granted under Title 35, U. S. Code (1952),

see. 266) The invention described herein may be manuiactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

The present invention is concerned with enhancing the resistance of red phosphorus to oxidation.

More particularly the invention is concerned with increasing the resistance of red phosphorus to oxidation when stored or kept for long periods of time either as such or in admixture with solid oxidizing agents, such as barium nitrate, lead peroxide, basic lead nitrate and other oxidizing agents, in the form of primers or priming compositions for small arms, pyrotechnic compositions, incendiary compositions and other inflammable compositions.

When the ordinary forms of pulverulent red phosphorus now appearing on the market are mixed with solid oxidizing agents in the preparation of primer, incendiary, pyrotechnic and other inflammable compositions, the stability of the prepared compositions on storage under various conditions of humidity and temperature is not entirely satisfactory. The red phosphorus undergoes partial oxidation, whereby acids containing phosphorus in their negative radicals are formed.

As pointed out in my co-pending application Serial No. 519,950, filed January 27, 1944, jointly a) with Martin S. Silverstein, small amounts of iron and copper in red phosphorus adversely affect the storage stability of primer, pyrotechnic, incendiary and other inflammable compositions containing red phosphorus. Copper or copper compounds in red phosphorus or iron compounds in red phosphorus, even though present in small amounts, act as oxidation catalysts or accelerators of oxidation of the red phosphorus under storage conditions as well as under test conditions with warm water moist air at atmospheric pressure, and under test conditions with water moist warm oxygen;under super atmospheric pressure.

Analyses of many samples of pulverulent red phosphorus sold on the market, and from various sources of supply, have revealed that they all contained iron and copper, that the iron content varied roughly from 200 to 700 parts of iron (calculated as Fe) per million parts of red phosphorus, and that the copper content may vary from 10 to 40 parts of copper (calculated as (In) per million parts of red phosphorus.

Among the objects of the inventions described in my above mentioned joint application for patent with Martin S. Silverstein, was the provision of a process for quickly and effectively removing iron from red phosphorus whose iron content is undesirably high. In contrast to this stated object, the object of the present invention is provision of a process for quickly and effectively removing either copper or copper and iron from red phosphorus, whereby its resistance to oxidation during storage under varying conditions of temperature and humidity is enhanced.

The treatment of red phosphorus to remove copper described in the present application may precede or follow the acid treatments described in my said joint application with Martin S. Silverstein, whereby both the iron and copper content may be lowered.

Although the process of the present application is mostly concerned with the removal of copper from pulverulent red phosphorus containing it in undesirable amounts, the process of removal of copper is also accompanied by some considerable removal of iron from red phosphorus, thus, for example, an iron content of 92 parts per mil ion of red phosphorus may be brought down to 37 parts of iron per million parts of red phosphorus.

In general, the process of the present invention comprises intimately contacting pulverulent red phosphorus containing copper or copper and iron with a hot aqueous solution of an alkali metal cyanide, for example sodium cyanide or potassium cyanide. The concentration of the alkali metal cyanide solution may vary within wide limits from very dilute solutions to saturated solutions. A water solution of sodium cyanide containing from 2 to 25 per cent sodium cyanide may be employed. An 8 per cent water solution of sodium cyanide at the boiling point of the solution has been found to give excellent results in the removal of copper from red phosphorus containing from 10 to 40 parts of copper per million parts of red phosphorus. The intimate contact between the red phosphorus and the cyanide solution is brought about advantageously by agitatin or vigorously stirring the solution containing the red phosphorus under treatment. When the solution is employed at the boiling temperature, the agitation due to boiling is usually suiiicient. When, however, the cyanide solution is employed at a temperature below the boiling point, intimate contact between the red phosphorus particles and the cyanide solution is attained by vigorous stirring or agitation of the solution.

The temperature of the cyanide solution during the treatment of the red phosphorus therewith may vary within wide limits, for example it may range from 50 C. to the boiling point of the solution at atmospheric pressure. The treatment .of the. 1'ed.phosphorus...with the cyanide solution may hes-performed at temperatures above the boiling point of the solution at atmospheric pressure by conducting the contact be. tween the red phosphorus and the cyanide solution under pressures above atmospheric-pressure accompanied by agitation of the red phosphorus in the solution to bring aboutintimate contact between the red phosphorus and the solution. As a general rule, the ratesof removal of the copper from the red phosphorus is directly proportional to the temperature of the -.oyanide.

solution, and the concentration of the cyanide solution.

To the aqueous solution of alkali metal cyanide used in the process there may be added a sufficient amount of alkali metal-hydroxide to appreciably reduce hydrolysis of the cyanide, whereby the liberation of hydrocyanicacid from thehot or boiling solutionis prevented-or. reduced. Thus,,the hydrolysis of a .Water solution of sodium cyanide may be retarded or arrested by theaddition of sodium hydroxide to the solu-- tion.

Ihe following; specific; examples are illustrative of the manner of praeticingthe invention.

Example I Pulverulent red phosphorus appearingnow on the market and containing more than 99 per cent of phosphorus after. washing and drying,

but still containing small quantities of iron and copper, was subjected to a sedimentation or separating operation to remove particles of less than 10. microns indiameter. The particles erred phosphorus of microns andabove were collected anddried and constituted the starting material for this and. succeeding examples. This startingmaterial contained more than 99. per cent. red phosphorus, but. there. was also contained in it 92 parts ofiron (calculated as Fe) per million parts of red phosphorus and 1.4 parts of. copper. (calculated as. Cu) per million parts of red phosphorus.

Three hundred grams of an 8.0 per cent water solutionof sodium cyanide Were heated to boiling. To the boiling solution of sodium cyanide there were added 100 grains of the red phosphorus starting material described above. The red phosphorus was added to-the boiling :solution at such a rate that the solution continued to boil during the additionsof the whole amount of red phosphorus.

continued during thetime required to add-the red phosphorus to the solution. Afterall of the 100 grams of red phosphorus were added to they cyanide solution, the boilingof the solution was continued for-thirty minutes. The heat applied in producing the boiling was sufiicient to produce boiling at such arate that the red phosphorus was thoroughly and continually agitated in the By proceeding in thismanner, the agitation of the. red phosphorus. in the solution When this 3.2 parts of copper (calculated as Cu) per million parts of red phosphorus. By comparing this analysis with the analysis of the starting material. it will be observed. that the copper content of the red, phosphorus was reduced and that also a portion'of theiron content hasbeen removed:

Example II Example HI Red. phosphorus treated according to Exampic I above phorus was subject to intimate contact andagitation with a dilute water solution of a mineral.

acid according to the process described in the above mentioned joint application for patent. The mineral acid may be sulphuric, hydrochloric, nitric or phosphoric acid. Either thewet or dry final product of Exampie I may be used as the starting material of this example.

The red phosphorus starting material. was mixed with a 10 per cent water solution of sulphuric acid in the ratio of one gram of red phos phorus to 5 milliliters of sulphuric acidv solution. The mixture was brought to boiling and the boiling continued for one hour. 'The boilingof the solution agitated the red phosphorus in the solution. volume with cold water, filtered and Washed with Water on the filter until free of acid. The washed and filtered red phosphorus was then dried in a vacuum oven at 60 C. The dried treated red phosphorus contained. only 2.5 parts of iron .per million parts of red phosphorus and 3.2 parts of copper per million parts of red phosphorus.

I claim:

1. Process for preparing red phosphorus of increased. resistance to oxidation from red phosphorus containing copper impurities, said process comprising intimately contacting the said impure red phosphorus With an aqueous solution of alkali metal cyanide for removing copper from the said red phosphorus, thereafter washing the.

red phosphorusto remove the cyanide solution and metal cyanide complexes therefrom, andv thereafter drying the thus purified and more. stable red phosphorus.

2. Process for preparing red phosphorus of in.- creased resistance to oxidation from .red phosphorus containing copper impurities in the order.

of ten toforty parts of copper per million parts of phosphorus, said process comprising the lowering of the copper content to the order of.

one to three parts per million parts of phosphorus by intimately contacting the said red phosphorus with a hot aqueous solution of. an alkali.

metal cyanide, thereafter Washing the red phosphorus to remove the cyanide solution andmetal cyanide complexes therefrom, and, thereafter drying the thus purified and more stable. red

phosphorus.

and containing 3'7 parts of iron and. 3.2 parts of copper per million parts of red phos- The mixture was then diluted to twice its.

3. Process for preparing red phosphorus of increased resistance to oxidation from red phosphorus containing copper impurities, in the order of ten to forty parts of copper per million parts of phosphorus, said process comprising the lowering of the copper content to the order of one to three parts per million parts of phosphorus by intimately contacting the said red phosphorus with a boiling aqueous solution of an alkali metal cyanide, thereafter washing the red phosphorus with water to remove the cyanide solution and metal cyanide complexes therefrom, and thereafter drying the thus purified and more stable red phosphorus.

4. Process for preparing red phosphorus of increased resistance to oxidation from red phosphorus containing copper impurities, said process comprising intimately contacting the said red phosphorus with an aqueous solution containing an alkali metal cyanide and an alkali metal hydroxide, thereafter washing the red phosphorus with water to remove the cyanide and alkali metal hydroxide solutions therefrom, and thereafter drying the thus purified and more stable red phosphorus.

5. Process for preparing red phosphorus of increased resistance to oxidation from red phosphorus containing copper impurities, said process comprising intimately contacting the said red phosphorus with an aqueous solution of an alkali metal cyanide, Washing with water to remove the metal cyanide complexes, then intimately contacting said red phosphorus with an aqueous solution of a mineral acid, thereafter washing the red phosphorus with water to remove the mineral acid and acid soluble salts therefrom, and thereafter drying the thus purified and more stable red phosphorus.

6. Process for preparing red phosphorus of increased resistance to oxidation from red phosphorus containing copper impurities, said process comprising intimately contacting the said red phorphorus with an aqueous solution of a mineral acid, washing with water to remove the acid and acid-soluble salts, then intimately contacting said red phosphorus with an aqueous solution of an alkali metal cyanide, thereafter washing the red phosphorus with water to remove the metal cyanide complexes therefrom, and thereafter drying the thus purified and more stable red phosphorus.

7. Process for preparing red phosphorus of increased resistance to oxidation from red phosphorus containing copper impurities, in the order of ten to forty parts of copper per million parts of phosphorus, said process comprising the lowering of the copper content to the order of one to three parts per million parts of phosphorus by intimately contacting the said red phosphorus with a hot aqueous solution of an alkali metal cyanide, washing with water to remove the metal cyanide complexes, then intimately contacting said red phosphorus with a hot aqueous solution of a mineral acid, thereafter washing the red phosphorus with water to remove the mineral acid and acid soluble salts therefrom, and thereafter drying the thus purified and more stable red phosphorus.

8. Process for preparing red phosphorus of increased resistance to oxidation from red phosphorus containing copper impurities, in the order of ten to forty parts of copper per million parts of phosphorus, said process comprising the lowering of the copper content to the order of one to three parts per million parts of phosphorus by intimately contacting the said red phosphorus with a hot aqueous solution of a mineral acid, washing with water to remove the acid and acid-soluble salts, then intimately contacting said red phosphorus With a hot aqueous solution of an alkali metal cyanide, thereafter washing the red phosphorus with water to remove the metal cyanide complexes therefrom, and thereafter drying the thus purified and more stable red phosphorus.

9. In the art of preparing compositions of matter containing red phosphorus utilizing as a starting material red phosphorus which contains in the order of ten to forty parts of copper per million parts of phosphorus, the method which comprises the lowering of the copper content to the order of one to three parts per million parts of phosphorus by treating said red phosphorus with alkali metal cyanide solution, then washing the red phosphorus with water to remove the cyanide solution and metal cyanide complexes therefrom, thereafter drying the red phosphorus, and thereafter incorporating said red phosphorus of lowered copper content into a composition of matter as an ingredient thereof.

10. In the art of preparing compositions of matter containing red phosphorus utilizing as a starting material red phosphorus which contains in the order of ten to forty parts of copper per million parts of phosphorus, the method which comprises the lowering of the copper content to the order of one to three parts per million parts of phosphorus by treating said red phosphorus with an aqueous solution of an alkali metal cyanide and an alkali metal hydroxide, then washing the red phosphorus with water to remove the cyanide solution and metal cyanide complexes therefrom, thereafter drying the red phosphorus, and thereafter incorporating said red phosphorus of lowered copper content into a composition of matter as an ingredient thereof.

GEORGE F. NORDBLOM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,178,081 Layng Apr. 4, 1916 OTHER REFERENCES Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 8, 1928, pp. 743, 745; Longmans, Green and Co., New York, N. Y.

Thorpes Dictionary of Applied Chemistry, Fourth Ed, vol. III, 1939, pp. 485, 486; Longmans, Green and Co., New York, N. Y. 

1. PROCESS FOR PREPARING RED PHOSPHORUS OF INCREASED RESISTANCE TO OXIDATION FROM RED PHOSPHORUS CONTAINING COPPER IMPURITIES, SAID PROCESS COMPRISING INTIMATELY CONTACTING THE SAID IMPURE RED PHOSPHORUS WITH AN AQUEOUS SOLUTION OF ALKALI METAL CYANIDE FOR REMOVING COPPER FROM THE SAID RED PHOSPHORUS, THEREAFTER WASHING THE RED PHOSPHORUS TO REMOVE THE CYANIDE SOLUTION AND METAL CYANIDE COMPLEXES THEREFROM, AND THEREAFTER DRYING THE THUS PURIFIED AND MORE STABLE RED PHOSPHORUS. 